1. Field of the Invention
The present invention relates to a press machine.
2. Discussion of the Background
Japanese Unexamined Patent Application Publication No. 2007-054844, for example, discloses a press machine in which a detector senses electrical conductivity to reliably detect a foreign object which is present between a stripper and a workpiece or a die, and the press operation is stopped at the same time as the detection of the foreign object.
As another example, Japanese Unexamined Patent Application Publication No. 7-275971 discloses the following technique. An abnormality detector for monitoring torque in a transfer apparatus actually measures a torque value in normal operation for each particular transfer pattern and sets the actually measured value as a reference torque value for the relevant pattern. An allowable torque range is calculated to specify an upper limit torque value and a lower limit torque value, which are obtained by adding and subtracting a preset deviation value to and from the reference torque value, and the calculated allowable torque range is stored in a control device. Whenever actual operation is performed in accordance with the pattern, an actual torque value is measured and compared with the allowable torque range. Further, the moment when the actual torque value exceeds the allowable torque range is detected.
As still another example, Japanese Unexamined Patent Application Publication No. 03-196313 discloses the following technique. A disturbance estimation observer is disposed in consideration of that intrusion of a foreign object can be regarded as a disturbance imposed on a servomotor. When the amplitude of an estimated disturbance exceeds a set value defined in advance, the estimated disturbance is detected as an actual disturbance.